You must contact the supplemental type certificate holder to seek written permission. The supplemental type certificate and its related information – all drawings, data, specifications – are the property of the supplemental type certificate holder. FAA will not release this information without authorization from the owner.
See 14 CFR § 21.120, Responsibility of supplemental type certificate holders to provide written permission for alterations.I can't find the supplemental type certificate holder. What do I do now?
If the mail you sent was returned "undeliverable" and there is no phone listing for the holder, please contact the issuing FAA office. Supplemental type certificates are approved and issued through the FAA Aircraft Certification Office (ACO) which serves the geographic area of the supplemental type certificate owner’s residence.Where can I find information about STCs installed on my aircraft?
If you need information about supplemental type certificates that have been installed on your aircraft, you may: